1. Field of the Invention
This invention relates to a method and device for guiding steel material to be rolled into a rolling mill machine for producing rolled steel products of various shapes such as wire rods, steel bars and H-section beams. More particularly, this invention relates to a method capable of making a more stiff steel material guiding device applicable to a low temperature hot rolling, high speed rolling and high load rolling for special steel, which have spread in the art tending to increase the load exerted on the steel material guiding device.
2. Description of the Prior Art
Conventionally, there have been known various types of steel material guiding devices such as of a roller guide type and a friction guide type. For instance, the conventional roller guide type guiding device shown in FIG. 3 comprises a pair of roller holders 1 having guide rollers 2 for guiding a steel material 3 to be rolled. The roller gap defined between the guide rollers 2 can be adjusted in accordance with the dimension of the steel material 3 by actuating a cylinder 4 to rotate the roller holders 1 about pivots 5, respectively.
On the present technological level in the art, the roller guide type steel material guiding device is essential for rolling rod, wire, bar and other section steel and has a long history. However, information data of actually measured data of a load which is exerted on the guide rollers when guiding ordinary steel materials to be rolled have not been disclosed at all. Furthermore, the load exerted on the guide rollers has never been systematically studied nor practically taken into consideration in guiding the steel materials to be rolled. That is to say, the design and use of the roller guide type guiding device have generally progressed in dependence on the experience of engineers skilled in the art.
The aforenoted load generated in the steel material guiding device may be summarized as follows:
The load F exerted on the guide roller in the steel material guiding device is increased up to the maximum load value FT which is obtained by calculating backwards the entire plastic torque T (theoretical value) determined in accordance with the sectional shape, size and resistance to deformation of steel materials to be rolled. The load F has been so far considered about 20% to 60% of the maximum load value FT as a matter of fact. Thus, it was thought that the guide roller type guiding device capable of tolerating the load of such a degree is sufficient and accordingly may be formed of a flexible structure. Under the existing circumstances, the idea of increasing the "rigidity" of the roller guide type guiding device has been scarcely allowed for up to now.
Nothing but Japanese Utility Model Post-examination Publication No. SHO 61-1929 discloses the "rigidity" of the roller guide type steel material guiding device. However, the technical idea of determining the most suitable increment of the roller gap formed between the guide rollers relative to the load exerted on the guide rollers is mentioned nowhere in the aforenoted Japanese publication and any other references so far published.
In recent years, the high-load rolling technique such as of a high-speed and/or low temperature hot rolling type has been advanced in order for achieving improvements in productivity, energy conservation, and rationalization of processing (e.g. adoption of an online process for heat treatment) in rolling steel materials and making high strength steel materials fit for practical use. Under such a severe condition of rolling, tilting of the steel material inevitably occurs frequently during the process of rolling and becomes a serious problem to be solved in the art of rolling.
The high quality rolled steel products having high accuracy in size and sectional shape and a faultless surface are strictly required of users today. Though the rolling mill machine has been improved so as to be made more stiff, thus markedly increasing the quality of the rolled steel products, the roller guide type guiding device has made little progress and still suffered disadvantages of failure of rolling the steel material, occurrence of dimensional discontinuity and defects such as surface defects in the product obtained finally.
These disadvantages are caused by the low rigidity of the roller guide type guiding device having a relatively flexible structure, which is deemed to cause the steel material to tilt while traveling through the guiding device under pressure. Since the guiding device shown in FIG. 3 is formed of the flexible structure as noted above, the steel material 3 to be rolled is disadvantageously guided on the tilt when being nipped between the guide rollers 2 as illustrated in FIG. 4.